It is well known to make elastomeric polyurethanes for various uses such as, e.g., roller covers for printing or other presses, impact-resistant coverings, gaskets, seals, etc. Typically, such polyurethanes can be produced by reacting essentially linear polyester or polyether prepolymer with at least one glycol or polyol suitable for cross-linking of the prepolymer, e.g. as described in U.S. Pat. No. 3,769,265 issued Oct. 30, 1973 to G. Grogler et al. As disclosed in that patent, plasticizers such as phthalic acid esters can be added in the preparation of such polyurethanes.
It has been found, however, that in extended storage or end use of many elastomeric polyurethanes, the polymer tends to harden, commonly to a degree which substantially impairs or even eliminates suitability of the polymer for its intended use as an elastomeric material. Hence it is highly desirable to provide a technique for inhibiting such hardening, and it is an object of this invention to provide such a technique. Another object is the provision of a polyurethane-plasticizing composition which inhibits undesired hardening of the polyurethane. Another object is an improved elastomeric polyurethane composition having an inhibited tendency toward such hardening. Other objects include improvements in the preparation of such polyurethanes whereby the resulting polymer is inhibited against such hardening. Additional objects will be apparent from the following disclosure in which all parts and percentages are by weight except where otherwise noted.